This application is based on and claims priority to Japanese Patent Application No. 11-111,324, filed Apr. 19, 1999, the entire contents of which is hereby expressly incorporated by reference.
1. Field of Invention
The present invention generally relates to attaching swing arms to all terrain vehicle frames. More particularly, the present invention relates to coupling forward ends of swing arms to rearward facing portions of such frames.
2. Description of Related Art
All terrain vehicles typically comprise a welded frame assembly to which a variety of components are mounted. For instance, the frame assembly may comprise a left side subassembly and a right side subassembly that are interconnected using cross members. Body panels, such as a front fender subassembly and a rear fender subassembly, are mounted to the frame in the relevant locations. In addition, the frame assembly generally defines an engine compartment within the two side subassemblies. An engine is mounted in the engine compartment and a transmission extends away from the engine. Generally, the transmission is substantially contained within a transmission case that can be integrally formed with a crankcase of the engine.
The all terrain vehicle can be supported by at least two wheels, and often is supported by four wheels. The wheels are connected to the frame assembly through related suspension systems. Generally speaking, the rear wheels are connected to the frame assembly with a rear arm, which is also known as a swing arm. The rear arm extends forward from a location proximate a rear axle and is pivotally connected to the frame assembly. The pivot point is positioned within a region that is encased by the frame assembly. For instance, a pair of down tubes generally define a rear end of the frame assembly and the pivot point is positioned forward of a plane defined through the two down tubes. The pivot point can be defined by brackets that secure the rear arm to the frame assembly.
Because the pivot point of the rear arm is located within the frame assembly, the rear arm must be sized and configured to pass between members of the frame assembly. For instance, the rear arm is often tapered from a portion having a width at least as wide as the frame assembly to a portion that will easily pass between the left side subassembly and the right side subassembly. Such a tapering reduces the strength, and can compromise the integrity, of the rear arm over extended periods of time. Furthermore, stress risers often need to be compensated for in the design of such tapered swing arms.
In addition to the above-discussed integrity issues, positioning the pivot location within an envelope defined by the frame assembly also has other readily identifiable downfalls. For instance, the length of the rear arm must be increased to properly reach to the pivot location if the wheel base length is maintained. In addition, the increased length reduces the strength of the rear arm and requires the rear arm to be strengthened in other manners, such as increasing material thickness or adding gussets. Thus, the longer arm will inevitably weigh more than a similarly designed shorter arm. Moreover, adding components relating to the suspension system into the engine compartment further crowds an already overly crowded region of the vehicle.
For at least these reasons, a new mounting arrangement is sought whereby the rear arm can be linked to the frame assembly. The new mounting arrangement should decrease the overall length of the rear arm while maintaining the wheel base length of the vehicle. In addition, the new mounting arrangement should position the suspension components in an area of the vehicle that is less crowded by other components.
Accordingly, one aspect of the present invention involves an all terrain vehicle comprising a frame having a pair of rear tubes, an upper portion and a lower portion. The rear tubes extend from the upper portion to the lower portion with a plane being defined through the rear tubes. At least one rear arm bracket is secured to a portion of the frame. A rear arm is coupled to the frame and extends rearward of the rear arm bracket. At least one rear wheel is supported by a rear portion of the rear arm. The rear arm is capable of articulating relative to the frame about a pivot axis and the pivot axis is disposed rearward of the plane.
Another aspect of the present invention involves an all terrain vehicle comprising a frame and a rear arm. A wheel axle is carried by the rear arm. Means for mounting the rear arm to the frame are provided between said rear arm and said frame. A front end of the rear arm is connected to the means for mounting and the means for mounting comprises a pivot pin that is positioned rearward of the frame.
A further aspect of the present invention involves an all terrain vehicle comprising a frame and a pair of rear arm brackets. Each of the rear arm brackets is secured to a portion of the frame. A rear arm is coupled to the frame and extends rearward of the rear arm brackets. The rear arm comprises a pair of forward tongues and at least one rear wheel axle being supported by a rear portion of the rear arm. The forward tongues are pivotally coupled to the corresponding rear arm brackets. The rear arm is capable of articulating relative to the frame about a pivot axis. An engine is disposed within the frame with a transmission being coupled to the engine. A drive shaft extends from the transmission to the at least one rear axle and a protective housing encases at least a portion of the drive shaft.